1. Field of the Invention
The present invention relates to a sidelight type backlight device used in, for example, a liquid crystal display or other liquid crystal display devices. The invention also relates to a liquid crystal display device provided with a backlight device.
2. Description of the Related Art
Conventionally, in a display for electronic appliances such as a portable computer, for example, a liquid crystal display is used in consideration of portable use. The liquid crystal display is composed of a liquid crystal panel, which is a non-luminous display device. Accordingly, the liquid crystal display device has a backlight device for illuminating the liquid crystal panel.
A portable electronic appliance is reduced in thickness. Hence, a sidelight type is used as the backlight device.
The sidelight type backlight device is generally provided with a light source and a light guide plate for guiding the light emitted from the light source to an entire liquid crystal panel region. An incident plane which receives the light emitted from the light source is formed at a side face of the light guide plate. An exit plane which emits the incident light from the incident plane is formed at an upper part of the light guide plate. The light source is, for example, a fluorescent lamp. The light source is disposed near the incident plane. This kind of backlight device is disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 10-40872.
Other backlight device uses a light-emitting diode (LED) as the light source. In this kind of backlight device, a red, blue, and green LED are contained in one housing to serve as an LED package, and a plurality of LED packages may be used.
When the red, blue and green LEDs are housed in one package, red, blue, and green are mixed. As a result, the light emitted from the LED package is white.
In a specific structure of the LED package thus configured, the LED package includes the housing, red, blue, and green LEDs.
The housing is made of a resin having enough reflectivity for mixing the colors of the light components emitted from the LEDs efficiently, and is formed in a so-called bathtub structure having a vertical wall surrounding the circumference. The LEDs are contained in the housing, and are disposed in a substantially triangular shape linking the LEDs so that the colors of the light components emitted from the LEDs may be mixed efficiently. The inside of the housing is sealed with a permeable resin so that the light components emitted from the LEDs may escape outside.
The LED packages are arranged in a row so that the positions sealed with the permeable resin (the inside openings surrounded by the vertical wall) may be directed to the incident plane of the light guide plate within the housing.
However, in the backlight device formed of plural LED packages having such configuration and arranged in one row, color fluctuation is likely to occur on the light guide plate. This point will be more specifically explained below.
As mentioned above, the housing of the LED package is a bathtub structure. Each LED is disposed to form a substantially triangular shape linking these LEDs. Accordingly, each LED is disposed at a position slightly shifted to either vertical wall in the housing.
As a result, in a plan view of LEDs (when the backlight device is seen from above), any of the LEDs is shifted to one side of the LED package array direction. For example, when the red LED is shifted to one side of the LED package array direction, the shape of the illumination range when the illumination range of red light emitted from the LED package is seen in a plan view is defined by a line linking the red LED in the LED package array direction in the vertical wall of the housing and the red LED close to it, and a line linking the red LED in the LED package array direction in the vertical wall and the red LED remote from it. The shape of the thus defined illumination range is a shape biased to the other side of the LED array direction.
To the contrary, in a plan view of the LED package, the shape of the illumination range of the LED, for example, a blue LED arranged at the opposite side of the red LED in the LED package array direction is biased to one side.
Hence, at one side of the LED package array direction, the red light hardly reaches the vicinity of the LED package, and at the other side, the blue right hardly reaches the vicinity of the LED package.
As a result, in the light guide plate, at one side of the LED array direction, the rate of blue light is higher, thus making color mixing difficult, and uneven color is likely to occur. Similarly, in the light guide plate, at the other side of the LED array direction, the rate of red light is higher, thus making color mixing difficult, and uneven color is likely to occur.
In the above explanation, the red and blue LEDs are spaced from each other in the LED array direction, but this is not a limited example. Uneven color is likely to occur if any one of the plural LEDs contained in the housing is biased to any position of the vertical wall.